fix(overlay): validate that ConnectedPositionStrategy positions are passed in correctly at runtime (#9466)

Since we have some cases where we pass in positions verbatim to the connected position strategy (the connected position directive), we could end up in a situation where the consumer passed in a set of invalid positions that don't break necessarily, but don't work correctly either. These changes add some sanity checks at runtime to make debugging easier.

src/cdk/overlay/position/connected-position-strategy.spec.ts

@@ -793,6 +793,60 @@ describe('ConnectedPositionStrategy', () => {
 
   });
 
+  describe('validations', () => {
+    let overlayElement: HTMLElement;
+    let originElement: HTMLElement;
+    let strategy: ConnectedPositionStrategy;
+
+    beforeEach(() => {
+      overlayElement = createPositionedBlockElement();
+      overlayContainerElement.appendChild(overlayElement);
+      originElement = createBlockElement();
+
+      strategy = positionBuilder.connectedTo(
+          new ElementRef(originElement),
+          {originX: 'start', originY: 'bottom'},
+          {overlayX: 'start', overlayY: 'top'});
+      strategy.attach(fakeOverlayRef(overlayElement));
+    });
+
+    afterEach(() => {
+      strategy.dispose();
+    });
+
+    it('should throw when attaching without any positions', () => {
+      strategy.withPositions([]);
+      expect(() => strategy.apply()).toThrow();
+    });
+
+    it('should throw when passing in something that is missing a connection point', () => {
+      strategy.withPositions([{originY: 'top', overlayX: 'start', overlayY: 'top'} as any]);
+      expect(() => strategy.apply()).toThrow();
+    });
+
+    it('should throw when passing in something that has an invalid X position', () => {
+      strategy.withPositions([{
+        originX: 'left',
+        originY: 'top',
+        overlayX: 'left',
+        overlayY: 'top'
+      } as any]);
+
+      expect(() => strategy.apply()).toThrow();
+    });
+
+    it('should throw when passing in something that has an invalid Y position', () => {
+      strategy.withPositions([{
+        originX: 'start',
+        originY: 'middle',
+        overlayX: 'start',
+        overlayY: 'middle'
+      } as any]);
+
+      expect(() => strategy.apply()).toThrow();
+    });
+  });
+
 });
 
 /** Creates an absolutely positioned, display: block element with a default size. */

src/cdk/overlay/position/connected-position-strategy.ts

@@ -15,6 +15,8 @@ import {
   OverlayConnectionPosition,
   ConnectedOverlayPositionChange,
   ScrollingVisibility,
+  validateHorizontalPosition,
+  validateVerticalPosition,
 } from './connected-position';
 import {Subject} from 'rxjs/Subject';
 import {Subscription} from 'rxjs/Subscription';
@@ -131,6 +133,7 @@ export class ConnectedPositionStrategy implements PositionStrategy {
       return;
     }
 
+    this._validatePositions();
     this._applied = true;
 
     // We need the bounding rects for the origin and the overlay to determine how to position
@@ -184,6 +187,8 @@ export class ConnectedPositionStrategy implements PositionStrategy {
       return;
     }
 
+    this._validatePositions();
+
     const originRect = this._origin.getBoundingClientRect();
     const overlayRect = this._pane.getBoundingClientRect();
     const viewportSize = this._viewportRuler.getViewportSize();
@@ -439,14 +444,28 @@ export class ConnectedPositionStrategy implements PositionStrategy {
     this._onPositionChange.next(positionChange);
   }
 
-  /**
-   * Subtracts the amount that an element is overflowing on an axis from it's length.
-   */
+  /** Subtracts the amount that an element is overflowing on an axis from it's length. */
   private _subtractOverflows(length: number, ...overflows: number[]): number {
     return overflows.reduce((currentValue: number, currentOverflow: number) => {
       return currentValue - Math.max(currentOverflow, 0);
     }, length);
   }
+
+  /** Validates that the current position match the expected values. */
+  private _validatePositions(): void {
+    if (!this._preferredPositions.length) {
+      throw Error('ConnectedPositionStrategy: At least one position is required.');
+    }
+
+    // TODO(crisbeto): remove these once Angular's template type
+    // checking is advanced enough to catch these cases.
+    this._preferredPositions.forEach(pair => {
+      validateHorizontalPosition('originX', pair.originX);
+      validateVerticalPosition('originY', pair.originY);
+      validateHorizontalPosition('overlayX', pair.overlayX);
+      validateVerticalPosition('overlayY', pair.overlayY);
+    });
+  }
 }
 
 /** A simple (x, y) coordinate. */

src/cdk/overlay/position/connected-position.ts

@@ -90,3 +90,29 @@ export class ConnectedOverlayPositionChange {
       /** @docs-private */
       @Optional() public scrollableViewProperties: ScrollingVisibility) {}
 }
+
+/**
+ * Validates whether a vertical position property matches the expected values.
+ * @param property Name of the property being validated.
+ * @param value Value of the property being validated.
+ * @docs-private
+ */
+export function validateVerticalPosition(property: string, value: VerticalConnectionPos) {
+  if (value !== 'top' && value !== 'bottom' && value !== 'center') {
+    throw Error(`ConnectedPosition: Invalid ${property} "${value}". ` +
+                `Expected "top", "bottom" or "center".`);
+  }
+}
+
+/**
+ * Validates whether a horizontal position property matches the expected values.
+ * @param property Name of the property being validated.
+ * @param value Value of the property being validated.
+ * @docs-private
+ */
+export function validateHorizontalPosition(property: string, value: HorizontalConnectionPos) {
+  if (value !== 'start' && value !== 'end' && value !== 'center') {
+    throw Error(`ConnectedPosition: Invalid ${property} "${value}". ` +
+                `Expected "start", "end" or "center".`);
+  }
+}